Dental filling materials mainly consist of liquid polymerizable organic monomers and/or polymers, reactive diluents, polymerization initiators, stabilizers, and fillers.
These composite materials have their good mechanical properties such as high flexural strengths, high compressive strengths and their hardness. Furthermore they are polishable and it is possible to adjust their dye. The most frequently used monomers are esters of methyacrylates and higher multifunctional alcoholes or isocyanates such as the bismethacrylate of biphenol-A diglycidyl ether, urethane bismethacrylates.
One of the main disadvantages using composites as dental filling materials is the relatively high shrinkage of organic monomers during polymerization. The shrinkage causes the well known effect of contraction gaps and subsequent cracks. Common dental composites show a shrinkage of 2.5 up to 4.0 vol.-%.
It is well known that the shrinkage directly depends on the molecular weight of polymerizable organic monomers. On the other hand, increasing molecular weights of the monomers are combined with an increasing viscosity of the resin. Therefore reactive diluents such as oligoethyleneglycoidimethacrylates, are necessary to obtain a lower viscosity and the possibility to incorporates the desired amount of fillers. However, reactive diluents show a relatively high shrinkage by themselves, for example 12.89 vol-% for pure triethyleneglycoldimethacrylate.
Moreover, conventional used composites snow a relatively low self-adhesion to teeth, metals are ceramics. In numerous experiments using epoxide polymers and methacryates for the preparation of IPNs (J. Polym. Sci. Part Al Polym. Chem. 30 (1992) 1941, J. Appl. Chrom. 24 (1991) 692, Polym. 31 (1990) 2066,) multiphase systems were obtained which have insufficient mechanical, thermal and optical properties or which result in microphase separated polymers (Acta Polymerica 38 (1987) 547 and DO 226731) with insufficient adhesion to teeth and ceramics.